A recent study of diet supplements conducted by the Harvard Medical School in Boston found that the amount of caffeine in the supplements varied widely and that the product labels were often inaccurate or contained no caffeine information at all. High levels of caffeine can can be dangerous for certain individuals, due to side effects such as tremors and anxiety. The study, published by JAMA Internal Medicine, tested 31 dietary supplements known to contain caffeine or herbal ingredients that naturally contain caffeine. Researchers found that of the products tested, five had labels with inaccurate caffeine information and another six did not have caffeine on their labels, but contained very high levels of caffeine; averaging between 210 and 310 milligrams per serving. To compare, an eight-ounce serving of coffee contains approximately 100 milligrams of caffeine. The study concluded that the levels of caffeine in the supplements would not be an issue on their own, but may cause problems for people who combine the diet products with energy drinks, coffee and other high-caffeine foods and beverages. More troublesome was the wide-spread inaccuracy of the labels, which make it nearly impossible even for users who read the product information to know what they are consuming. The researchers added that current laws regulating product labeling aren’t strong enough and that the U.S. Food and Drug Administration (FDA) must do a better job enforcing what labeling regulations exist.